1. Field of the Invention
The present invention relates to a stroke-variable engine, and particularly to an improvement in a stroke-variable engine comprising: a main connecting rod connected at one end to a piston through a piston pin; a subsidiary connecting rod which is connected to a crankpin of a crankshaft rotatably supported in a crankcase of an engine body and which is connected to the other end of the main connecting rod; a control rod connected at one end to the subsidiary connecting rod at a position offset from a connected position of the main connecting rod; and a pivot shaft which is rotated about an eccentric axis by a power transmitted at a reduction ratio of 1/2 from the crankshaft and to which the other end of the control rod is connected.
2. Description of the Related Art
Such a stroke-variable engine is already known, for example, from Japanese Patent Application Laid-open No. 9-228858, Specification of U.S. Pat. No. 4,517,931 and the like, and designed so that intake and compression strokes and expansion and exhaust strokes are made different from each other by connecting one end of a control rod to a subsidiary connecting rod, and connecting the other end thereof to a pivot shaft rotated about an eccentric axis by a power transmitted from a crankshaft at a reduction ratio of 1/2.
However, in such a stroke-variable engine, a link mechanism comprises a main connecting rod connected to a piston, a subsidiary connecting rod connected to a crankpin of a crankshaft and connected to the other end of the main connecting rod, and a control rod which is connected at one end to the subsidiary connecting rod at a position offset from a connected position of the main connecting rod and connected at the other end thereof to a pivot shaft; and performs a motion of one cycle in two rotations of the crankshaft. Therefore, a 0.5-order inertial vibration is generated, and when a vibrating force provided by the 0.5-order inertial vibration is increased, the following problem is provided:
With an increase in inertial vibration due to an excessively large inertial force, the vibration of the engine is increased and noise due to the vibration is generated. Therefore, there is a need for a measure for avoiding a reduction in strength of engine components due to the excessively large inertial force. Further, mountability of the engine to a working machine is deteriorated due to the excessively large inertial force.